Planetary atmospheres Earth

Lange, M. A., Ahrens, T. I. (1986) Shock-induced C02 loss from CaC03 Implications for early planetary atmospheres. Earth Planet. Sci. Lett., 77, 409-18. 

Of the alkenes (Figure 5.5) only ethene has been detected and of the aromatics only benzene has been seen unambiguously surprisingly propene has not been seen despite its well-understood microwave spectrum. Of interest to the origins of life is the onset of polymerisation in HCN to produce cyanopolyynes. These molecules could provide a backbone for the formation of information-propagating molecules required for self-replication. The survival of these species in a planetary atmosphere depends on the planet oxidation would be rapid in the atmosphere of today s Earth but what of the early Earth or somewhere altogether more alkane-based such as Titan ... 

Meteoroid - the name given to a meteorite or a meteor before it enters the Earth s (or any other planetary) atmosphere. 

The rate of photolysis, J, depends on the absorption cross-section, a, the number density, the scale height and the angle, all of which are unique properties of a planetary atmosphere. For the Earth and the Chapman mechanism for ozone the O3 concentration maximum is 5 x 1012 molecules cm-3 and this occurs at 25 km, shown in Figure 7.12, and forms the Chapman layer structure. 

Noble gases are most abundant in planetary atmospheres, although even there they are only minor components. They have been measured in the gas envelopes of Venus, Earth (of course), Mars, and Jupiter. We will consider their utility in understanding planetary differentiation and atmospheric evolution shortly, but first we will focus on their rather miniscule abundances in meteorites and other extraterrestrial materials. 

Noble gases may provide a constraint on the source of water and other volatiles. The abundance pattern of noble gases in planetary atmospheres resembles that of chondrites, perhaps arguing against comets. However, there are some differences, especially in the abundance of xenon. Relative to solar system abundances, krypton is more depleted than xenon in chondrites, but in the planets, krypton and xenon are present in essentially solar relative abundances (Fig. 10.11). This observation has been used to support comets as the preferred source of volatiles (even though measurements of xenon and krypton in comets are lacking). A counter-argument is that the Ar/H20 ratio in comets (if the few available measurements are accurate and representative) limits the cometary addition of volatiles to the Earth to only about 1%. 

The necessary starting point for any study of the chemistry of a planetary atmosphere is the dissociation of molecules, which results from the absorption of solar ultraviolet radiation. This atmospheric chemistry must take into account not only the general characteristics of the atmosphere (constitution), but also its particular chemical constituents (composition). The absorption of solar radiation can be attributed to carbon dioxide (C02) for Mars and Venus, to molecular oxygen (02) for the Earth, and to methane (CH4) and ammonia (NH3) for Jupiter and the outer planets. 

The development of the relationships between scattered light and aerosols has stimulated the use of radiation transfer theory for remote sensing of particles in planetary atmospheres. Highly sophisticated experimental and theoretical techniques have emerged for the interpretation of observations of sunlight and artificial light sources in the earth s atmosphere. A description of their application depends on further development of the concepts of radiant energy transfer. 

Argon is an important element for nucleosynthesis, for the discovery and interpretation of isotopic anomalies, and for the interpretation of the origin of planetary atmospheres. Argon is the eleventh most abundant element in the universe thus it is an important datum for nucleosynthesis theories. It is much rarer in terrestrial abundances because most Ar was lostinto space (owing to its inertness and high volatility) as the Earth formed. 

Marti K. and Mathew K. (1998) Noble-gas components in planetary atmospheres and interiors in relation to solar wind and meteorites. Proc. Indian Acad. Sci. Earth Planet Sci. 107, 425-431. 

Ahrens T. J. (1993) Impact erosion of terrestrial planetary atmospheres. Ann. Rev. Earth Planet. Sci. 21, 525-555. 

Sulfuric acid is an important component of upper planetary atmospheres. The background sulfur found in the Earth s stratosphere derives... 

Ip and Fernandes [ 101] calculated that 6x lO to 6x lO s g of cometry material could liave been delivered to Earth at the time of the formation of the great Oort Cloud of comets. This amount is equivalent to 4-40 times the present mass of the oceans, assuming about 50% of the cometaiy mass is ice. Owen and Bar-Nun [102] examined tlie ability of amorphous ice formed at temperatures below lOOK to trap ambient gases. By comparison of the compositions of gases trapped by ice with tlie compositions of the interstellar medium, comets, and planetary atmospheres, Owen and Bar-Nun [102] concluded that icy comets delivered a considerable fraction of the volatiles to the imier planets. Owen [83] emphasized that Uie potential supply of cometaiy materials is more than adequate. 

Sasaki, S. Nakasawa, K. 1988. Origin of isotopic fractionation of terrestrial Xe, hydrodynamic fractionation during escape of the primordial H2-He atmosphere. Earth and Planetary Science Letters, 89, 323-334. 

Lecuyer, C. Ricard, Y. 1999. Long-term fluxes and budget of ferric iron implication for the redox state of the Earth s mantle and atmosphere. Earth and Planetary Science Letters, 165,197-211. 

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